So the mediator trait is a very interesting one, and it appeals to many an enchantment sorceror, wizard, and also the bread and butter of mesmerists. That said, there's occasional talk of what spells count as acceptable for the trait bonus for the spell DC.
This comment laid things out pretty nicely, but it looks to have been forgotten in the wind.
Trait in Question: Mediator (Champions of Purity) : You receive a +1 trait bonus to the DC of any charm or compulsion effect that does not provide ongoing control and results in peaceful acts, such as calm emotions, sleep, or a suggestion to lay down arms.
So the crux of its usage is two-fold.
1. Does not provide ongoing control.
This portion reasonably kicks spells such as charm XYZ and dominate XYZ spells.
2. Results in peaceful acts.
This calls into question what a peaceful act is.
Peaceful on an individual basis, much like how many of these sorts of spells are cast, varies based upon the individual's perspective.
It can reasonably argued that a state of inaction is more peaceful than say smacking some goblin with a billy club. It can also be argued that a target laughing maniacally on the ground is more peaceful than that same fellow shooting your ally with a crossbow
Finally, we come to the example spells provided: "such as calm emotions, sleep, or a suggestion to lay down arms."
Calm emotions denies the use of morale bonuses, prevents barbarians from raging, etc. It is a denial of specified actions, and this denial is then considered a peaceful act. With this in mind, an easy argument for spells such as hideous laughter and daze, which both deny actions, to be considered peaceful spells.
Sleep denies actions and even makes the targets helpless, which is an even larger than denial of actions than either hideous laughter or daze, or even hold XYZ for that matter. Sleep also has a longer duration than the sum of these spells' durations combined (for a given caster level).
Suggestion is follows a similar train of thought (see what I did there?) as spells like sow thought, modify memory, etc. None of these grant ongoing control, and all of them can be used to bring forth peaceful acts.
To conclude, I'd appreciate it if we could get some dialogue and some quality consensus going on this fun trait.
Disclosure: I'm biased and want to use this on enchantment sorcerors and mesmerists.
I believe that the DC of suggestion would increase as it's called out in the spell. Although this depends on how you use it. I don't think it would work for Hold X spells, but it would work for Daze as it's very similar to sleep.